Frequency spectrum detection system

Abstract

A frequency spectrum detection system including: a frequency-scan light source, a phase modulator, an optical filter, an optical fiber, a photodetector, a power divider, an electric amplifier, a combiner, an electric filter, and an oscilloscope. The frequency-scan light source, the phase modulator, the optical filter, the photodetector, and the electric amplifier form a ring-shaped optoelectronic oscillator resonant cavity, which is configured to generate a frequency-scan signal. The combiner is configured to receive a signal to be measured. The phase modulator is configured to modulate the combined electrical signal onto a frequency-scan optical signal. The optical filter is configured to selectively attenuate or amplify one sideband of double sidebands of the double-sideband phase-modulated optical signal. The photodetector is configured to detect a signal filtered by the optical filter.

What is claimed is: 
     
       1. A frequency spectrum detection system, comprising: a frequency-scan light source, a phase modulator, an optical filter, an optical fiber, a photodetector, a power divider, an electric amplifier, a combiner, an electric filter, and an oscilloscope, wherein,
 a ring-shaped optoelectronic oscillator resonant cavity is defined by the frequency-scan light source, the phase modulator, the optical filter, the optical fiber, the photodetector, and the electric amplifier together, the optoelectronic oscillator resonant cavity being configured to generate a frequency-scan signal with adjustable bandwidth and adjustable center frequency when a Fourier domain mode-locking condition is satisfied; 
 the combiner is configured to receive a signal to be measured, and to combine the signal to be measured with a frequency-scan signal generated by self-excited oscillation in the optoelectronic oscillator resonant cavity to form a combined electrical signal, the combined electrical signal being input into an electrical signal input terminal of the phase modulator; 
 the phase modulator is configured to modulate the combined electrical signal, which is input through the electrical signal input terminal, onto a frequency-scan optical signal emitted from the frequency-scan light source, and is configured to output a double-sideband phase-modulated optical signal; 
 the optical filter is configured to selectively attenuate or amplify one sideband of double sidebands of the double-sideband phase-modulated optical signal; 
 the photodetector is configured to detect a signal filtered by the optical filter; 
 the photodetector, the power divider, the electric amplifier, the combiner, and the phase modulator are connected through cables; and 
 the power divider, the electric filter, and the oscilloscope are connected through cables. 
 
     
     
       2. The frequency spectrum detection system according to  claim 1 , wherein the frequency-scan light source is a current-driven frequency-scan semiconductor laser or a single-sideband-modulation-based frequency-scan light source, and the frequency-scan light source has an emission wavelength which is changed periodically. 
     
     
       3. The frequency spectrum detection system according to  claim 1 , wherein the optical filter is a notch optical filter, or an optical filter based on a stimulated Brillouin scattering effect gain spectrum. 
     
     
       4. The frequency spectrum detection system according to  claim 1 , wherein,
 the frequency-scan light source, the phase modulator, the optical filter, and the photodetector together form a microwave photonics filter, and 
 the microwave photonics filter has a frequency-scan period that matches a time delay due to a single pass of signals in a loop of the optoelectronic oscillator resonant cavity, which satisfies the following Fourier domain mode-locking condition:
     nT=T   r ; 
 
 wherein, n is a positive integer, T is a period of change of the microwave photonics and T r  is the time delay due to a single pass of the signals in the loop of the optoelectronic oscillator resonant cavity. 
 
     
     
       5. The frequency spectrum detection system according to  claim 1 , wherein the frequency spectrum detection system is configured to implement frequency spectrum detection in different frequency measurement ranges by changing a magnitude relationship between a frequency of the frequency-scan signal, a frequency of the signal to be measured and a center frequency of the electric filter. 
     
     
       6. The frequency spectrum detection system according to  claim 1 , wherein the frequency spectrum detection system further comprises a polarization controller for controlling a polarization state of optical signals. 
     
     
       7. The frequency spectrum detection system according to  claim 1 , wherein the frequency spectrum detection system further comprises an optical amplifier or a second electric amplifier for amplifying signals. 
     
     
       8. The frequency spectrum detection system according to  claim 1 , wherein the loop of the optoelectronic oscillator resonant cavity comprises a single loop or multiple loops.